The present invention relates generally to an internal combustion engine employing coal-water slurry as the fuel, more particularly, to such an engine wherein a minor portion of each charge of the coal-water slurry fuel is injected into a pilot chamber and ignited to provide a stream of hot combustion gases for igniting the balance of the coal-water slurry fuel charge directly injected into the main combustion chamber of the engine.
Compression engines, i.e., diesel engines as pioneered by Rudolph Diesel, have long been utilized in the transportation field as well as in utility and industrial applications. The utilization of coal as the fuel for such engines has been a goal sought after since the conception of the diesel engine. While no basic thermodynamic reasons exist which would prevent the operation of a diesel engine with coal as the fuel, there were many mechanically and operational problems that had to be overcome before commercially viable coal-fuel diesel engines could be provided. For example, the erosive nature of the coal particulates in coal fuels in slurry or powder form have been found to cause a considerable impact on the durability of engine components contacted by the fuel. Also, the emission of sulfur oxides and particulates from coal-fueled engines were found to cause environmental pollution problems.
However, fairly recent developments in materials useful for fabrication of engine components contacted by the fuel have largely overcome the engine component durability problems. Further, recent developments in the preparation of the coal fuel and the developments in exhaust gas filtering mechanisms have significantly reduced the environmental problems. Even with such recent developments there is still a significant concern with respect to the use of coal as the fuel in diesel engines that has nor been adequately addressed. More specifically, in order to ignite the air and coal-fuel mixture in the engine, the air-fuel mixture must be heated to a temperature corresponding to a minimum threshold temperature required for the ignition of the fuel-air mixture. Several approaches to achieving this goal have met with various degrees of success. One such approach is the utilization of dual fuel engines in which a fuel other than the coal is ignited in the main chamber just prior to injection of the coal into the same main chamber thus providing an environment of hot combustion gases for igniting the air and coal mixture introduced into the same main combustion chamber. In some recently developed engines employing precombustion chambers, known as indirect firing, fired with an alternate fuel such as diesel fuel, there is sufficient heat retained in the engine components defining the main combustion chamber with the engine at substantially full load to operate the engine without the pilot ignition. Another approach to the use of coal as the fuel in a diesel engine is the use of a hot insulated pre-chamber in communication with the main combustion chamber into which the entire charge of coal in powder form is mixed with the intake air, this is again referred to as indirect firing. A portion of this air-coal mixture is forced into the hot prechamber during compression stroke to initiate the combustion process. In still another approach the entire charge of coal in powder form is injected into a precombustion chamber for admixture and ignition with air heated by compression and the hot walls of the engine components. While the aforementioned engines have provided significant improvements in the use of coal as the fuel, some decreases in combustion efficiencies occur. For example, engines with pre-chamber combustion chambers wherein all of the charge is introduced into the chamber, efficiency losses occur because of the higher heat transfer losses due to the larger surface area employed with respect to engines not employing precombustion chambers. Also, in the previous engines using prechambers, throttle losses are present in the throat or passageway between the pre-chamber and the main chamber that are not present in direct injected engines. Scheduling losses are also present due to the timing of the combustion process.